Dr. Aly, O.
Computer Science

Introduction

The purpose of this discussion is to elaborate on the previous discussion of the Encryption  and discuss the functionality provided by the public key encryption and public key infrastructure (PKI).

Public Key Infrastructure (PKI)

The PKI is a framework which enables the integration of various services which are related to cryptography. The purpose of the PKI is to provide confidentiality, integrity, access control, authentication and most importantly non-repudiation.  The encryption/decryption, digital signature, and key exchange are the three primary functions of the PKI (Srinivasan, 2016).

There are three major functional components to the PKI.  The first component involves The Certificate Authority (CA), an entity which issues certificates. One or more in-house servers, or a trusted third party such as VeriSign or GTE, can provide the CA function.  The second component involves the repository for keys, certificates, and Certificate Revocation List (CRLs), which is usually based on a Light-weight Directory Access Protocol (LDAP)-enabled directory service.  The third component involves the management function, which is typically implemented via a management console (RSA, 1999).  Moreover, if the PKI provides automated key recovery, there may also be a key recovery service. The Key Recovery is an advanced function required to recover data or messages when a key is lost.  PKI may also include Registration Authority (RA) which is an entity dedicated to user registration and accepting requests for certificates.  The user registration is the process of collecting information of the user and verifying the user identity, which is then used to register the user according to a policy.  This process is different from the process of creating, signing, and issuing a certificate.  For instance, the Human Resources department may manage the RA function, while the IT department manages the CA.  Moreover, a separate RA makes it harder for any single department to subvert the security system.  Organizations can choose to have registration handled by a separate RA, or included as a function of the CA.  Figure 1 illustrates the main server components of a PKI; certificate server, certificate repository, and key recovery server accompanied with management console, as well as PKI-enabled applications building blocks (RSA, 1999).

Figure 1.  The Main Server Components of PKI (RSA, 1999).

PKI Standards

The PKI standards permit multiple PKIs to interoperate, and multiple applications to interface with a single, consolidated PKI.  The PKI standards are required for enrollment procedures, certificate formats, CRL formats, certificate enrollment messages formats, digital signature formats, and challenge and response protocols.  The primary focus of interoperable PKI standards is the PKI working group of the Internet Engineering Task Force (IETF), also known as the PKIX group for PKI for X.509 certificates (RSA, 1999).  The PKIX specification is based on two other standards X.509 from the International Telecommunication Union (ITU) and the Public Key Cryptography Standards (PKCS) from RSA Data Security (RSA, 1999). 

Standards Rely on PKI

There are standards which rely on PKI.  Most major security standards are designed to work with PKI.  Secure Socket Layer (SSL) and Transport Layer Security (TLS), which are used to secure access to Web servers and web-based applications, rely on PKI.  The Secure Multipurpose Internet Mail Extensions (S/MIME), which is used to secure messaging rely on PKI.  The Secure Electronic Transaction (SET) to secure bank card payments, and  IPSEC to secure connection using VPN require PKI (Abernathy & McMillan, 2016; RSA, 1999; Stewart, Chapple, & Gibson, 2015).

The PKI Functions

The most common PKI functions are issuing certificates, revoking certificates, creating and publishing CRLs, storing and retrieving certificates and CRLs, and key lifecycle management.  The enhanced and emerging functions of PKI include the time-stamping and policy-based certificate validation.  The summary of the PKI functions is illustrated in Table 1, adapted from (RSA, 1999). 

Table 1.  PKI Functions (RSA, 1999).

Public Key Encryption

In 1976, the idea of public key cryptography was first presented in Stanford University by Martin Hellman, Ralph Merkle, and Whitfield Diffie (Janczewski, 2007; Maiwald, 2001; Srinivasan, 2016).  There are three requirements for the public key encryption method.  When the decryption process is applied to the encrypted message, the result must be the same as the original message before it was encrypted.  It must be exceedingly difficult to deduce the decryption (private) key from the encryption (public) key.  The encryption must not be able to be broken by a plaintext attack. Since the encryption and decryption algorithms and the encryption key will be public, people attempting to break the encryption will be able to experiment with the algorithms to attempt to find any flaws in the system (Janczewski, 2007).

One popular method of the public key encryption was discovered by a group of MIT in 1978 and was named RSA after the initials of the three members of the group Ron Rivest, Adi Shamir, and Leonard Adleman (Janczewski, 2007).   The RSA Algorithm was patented by MIT, and then this patent was handed over to a company in California called Public Key Partners (PKP), which holds an exclusive commercial license to sell and sublicense the RSA public key cryptosystem.  PKP also holds other patents which cover public key cryptography algorithm.  RSA encryption can be broken based on factoring numbers involved, which can be ignored due to the massive amount of time required to factor large numbers.   However, RSA is too slow for encrypting large amounts of data.  Thus, it is often used for encrypting the key used in a private key method such the International Data Encryption Algorithm (IDEA) (Janczewski, 2007).

The main difference between the symmetric key encryption and the public key encryption is the number of keys used in operation.  The symmetric key encryption utilizes a single key both to encrypt and decrypt information, while the public key encryption utilizes two keys, one key is used toencrypt, and a different key is then used to decrypt the information (Maiwald, 2001).  Figure 2 illustrates the primary public key or asymmetric encryption operation.  Both the sender and receiver must have a key. The keys are related to each other and called key pair, but they are different.  The relationship between the keys is that the information encrypted by one key can be decrypted by the other key.  One key is called private, while the other key is called public.  The private key is kept secret by the owner of the key pair.  The public key is published with information about who the owner is.  It is published as public because there is no way to publish a private key from it.

Figure 2.  Public Key Encryption Operation (Maiwald, 2001).

The encryption is performed with the public key, where only the owner of the key pair can decrypt the information since the private key is kept secret by the owner if the confidentiality is desired.   The owner of the key pair encrypts the information with the private key if authentication is desired.   The integrity of the information can be checked if the original information was encrypted with the private key of the owner (Maiwald, 2001; Stewart et al., 2015).

The asymmetric key cryptography or public key encryption provides an extremely flexible infrastructure, facilitating simple, secure communication between parties that do not necessarily know each other before initiating the communication.  The public key encryption also provides the framework for the digital signing of messages to ensure non-repudiation and message integrity.  It also provides a scalable cryptographic architecture for use by large numbers of users).  The significant strength of the public key encryption is the ability to facilitate communication between parties previously unknown to each other.  This process is made possible by PKI hierarchy of trust relationships.  These trusts permit combining asymmetric cryptography with symmetric cryptography along with hashing and digital certificates, providing hybrid cryptography (Abernathy & McMillan, 2016; Maiwald, 2001; Stewart et al., 2015)

The limitation of the public key encryption is that they tend to be computationally intensive and thus are much slower than symmetric key systems.  However, if the public key is teamed with the symmetric key encryption, the result is the much stronger system. The public key system is used to exchange keys and authenticate both ends of the connection.  The symmetric key system is then used to encrypt the rest of the traffic as it is faster than the public key system (Abernathy & McMillan, 2016; Maiwald, 2001; Stewart et al., 2015).

References

Abernathy, R., & McMillan, T. (2016). CISSP Cert Guide: Pearson IT Certification.

Janczewski, L. (2007). Cyber warfare and cyber terrorism: IGI Global.

Maiwald, E. (2001). Network security: a beginner’s guide: McGraw-Hill Professional.

RSA. (1999). Understanding Public Key Infrastructure (PKI). Retrieved from ftp://ftp.rsa.com/pub/pdfs/understanding_pki.pdf, White Paper

Srinivasan, M. (2016). CISSP in 21 Days: Packt Publishing Ltd.

Stewart, J., Chapple, M., & Gibson, D. (2015). ISC Official Study Guide.  CISSP Security Professional Official Study Guide (7th ed.): Wiley.

Dr. Aly, O.
Computer Science

Introduction

The purpose of this discussion is to discuss and analyze encryption, the encryption types, the impact of the encryption, and the use of encryption when streaming data in the network.

Cryptography and Encryption

The cryptography comprises a set of algorithms and system-design principles, some well-developed and some are just emerging for protecting data in the era of Big Data and Cloud Computing.  Cryptography is a field of knowledge whose products are encryption technology.  Encryption technology is an inhibitor to compromising privacy with well-designed protocols.  However, it is not the “silver bullet” to cut through the complexity of the existing issues of privacy and security (PCAST, May 2014).

The encryption technology involves the use of a key. Only with the key can encrypted data be used. At every stage of the life of the key, it is potentially open to misuse that can ultimately compromise the data which the key was intended to protect. If the user with access to private keys can be forced into sharing them, no system based on encryption is secure.

The keys were distributed physically, on paper or computer media, protected by registered mail, armed guards until the1970s.  However, the intervention of the “public-key cryptography” changed everything.  The public-key cryptography allows individuals to broadcast their personal key publicly.  However, this public key is only an encryption key, useful for turning plaintext into cryptotext which is meaningless to others.   The private key is used to transform cryptotext to plaintext and is kept secret by the recipient (PCAST, May 2014).  

The message typically is in the form of plaintext represented by the letter P when encryption functions are described.  The sender of the message uses a cryptographic algorithm to encrypt the plaintext message and generate a ciphertext or cryptotext represented by the letter C.  The message is transmitted, and the recipient uses a predetermined algorithm to decrypt the ciphertext message and retrieve the plaintext version.   All cryptographic algorithms rely on keys to maintain their security.  A key is just a number and usually substantial binary number.  Every algorithm has a specific “keyspace,” which is the range of values which are valid for use as a key for a specific algorithm and is defined by its “bit size.”  Thus, 128-bit key can have a value from 0 to 2¹²⁸.  It is essential and critical to protecting the security of the secret keys because of the security of the cryptography relies on the ability to keep and maintain the keys used privately (Abernathy & McMillan, 2016; Maiwald, 2001; Stewart, Chapple, & Gibson, 2015).  Figure 1 illustrates the basic encryption operation (Maiwald, 2001). 

Figure 1.  Basic Encryption Operation (Maiwald, 2001).

The modern cryptosystems utilize computationally sophisticated algorithm and long cryptographic keys to meet the cryptographic four goals mentioned below.  There are three types of an algorithm which are commonly used:  symmetric encryption algorithm, asymmetric encryption algorithm, and hashing algorithms (Abernathy & McMillan, 2016; Connolly & Begg, 2015; Stewart et al., 2015; Woo & Lam, 1992).

Four Goals for Encryption

The cryptography provides an additional level of security to the data during processing, storage, and communications.  A series of increasingly sophisticated algorithms have been designed to ensure the confidentiality integrity, authentication, and non-repudiation.  At the same time, hackers also have devoted time to undermine this additional security layer of the encryption.  There are four fundamental goals for organizations to use the cryptographic systems; the confidentiality, the integrity, the authentication, and non-repudiation.   However, not all of the cryptosystems are intended to achieve all four goals (Abernathy & McMillan, 2016; Stewart et al., 2015). 

The confidentiality ensures that the data remains private while at rest, such as when stored on a disk, or in or transit such as during transmission between two or more parties.  The confidentiality is the most common reason for using the cryptosystems. There are two types of cryptosystems which enforce confidentiality; symmetric key and asymmetric key algorithms.  The symmetric key cryptosystems use a shared secret key available to all users of the cryptosystem.  The asymmetric key algorithm uses special combinations of public and private key for each user of the system (Abernathy & McMillan, 2016; Stewart et al., 2015). 

When implementing a cryptographic system to provide confidentiality, the data types must be considered, whether the data is at rest or in motion.  The data at rest is the data that is stored in a storage area waiting to be accessed.  For instance, the data at rest include data stored on hard drives, backup tapes, cloud storage services, USB devices and other storage media.  The data in motion or data “on the wire” is the data that is being transmitted across the network between systems the data in motion might be traveling on a corporate network, a wireless network, or public Internet.  Both types of the data post different types of confidentiality risks against which cryptographic system can protect.  For instance, the data in motion may be susceptible to eavesdropping attacks, while data at rest is more susceptible to the theft of physical devices (Abernathy & McMillan, 2016; Stewart et al., 2015).

The integrity ensures that the data is not modified without authorization.  If the integrity techniques are in place, the recipient of a message can ensure that the message received is identical to the message sent.  The integrity provides protection against all forms of modification such intentional modification by a third party attempting to insert false information, and unintentional modification by faults in the transmission process.  The message integrity is enforced through the use of encrypted message digests, known as digital signatures created upon transmission of a message.  The integrity can also be enforced by both public and secret key cryptosystems (Abernathy & McMillan, 2016; Stewart et al., 2015).

The authentication is a primary function of the cryptosystems and verifies the claimed identity of system users.  Secret code can be used for the authentication.  The nonrepudiation assures the recipient that the message was originated by the sender and not someone masquerading as the sender.  Moreover, the nonrepudiation also prevents the sender to deny sending the message or repudiating the message. The secret key or symmetric key cryptosystems do not provide this guarantee of non-repudiation.  The non-repudiation is offered only by the public key or asymmetric cryptosystem (Abernathy & McMillan, 2016; Stewart et al., 2015).

Symmetric Cryptosystem

The symmetric key algorithms rely on a “shared secret” encryption key which is distributed to all users who participate in the communication.  The key is used by all members to both encrypt and decrypt messages.  The sender encrypts with the shared key, and the receiver decrypts with the same shared key. The symmetric encryption is difficult to break because of the long and large-size key. The symmetric encryption is primarily used for bulk encryption and to meet the confidentiality goal. The symmetric key cryptography can also be called “secret key cryptography and private key cryptography.”  There are several common symmetric cryptosystems such as the Data Encryption Standard (DES), Triple DES (3DES), International Data Encryption Algorithm (IDEA), Blowfish, Skipjack, and the Advanced Encryption Standard (AES).  The advantage of the symmetric cryptosystem is that it operates at high speed and it is faster than the asymmetric (1,000 to 10,000 faster) (Abernathy & McMillan, 2016; Connolly & Begg, 2015; Maiwald, 2001; Stewart et al., 2015).  

The symmetric cryptosystem has limitations.  The first limitation is the key distribution. The members must implement a secure method of exchanging the shared secret key before establishing the communication with the symmetric key protocol.  If the secure electronic channel does not exist, an offline key distribution method must be used.  The second limitation represents the nonsupport to the non-repudiation, due to sharing the same key which makes it difficult to know the source of the message. The third limitation represents the inability of the scalable algorithm.  The last limitation of the symmetric cryptosystem is the frequent regeneration of the key (Abernathy & McMillan, 2016; Connolly & Begg, 2015; Stewart et al., 2015). 

Asymmetric Cryptosystem

The asymmetric key algorithm, also known as “public key algorithm, provides a solution to the limitation of the symmetric key encryption.  This system uses two keys; a public key which is shared with all users, and a private key which is secret and known only to the user.  If the public key encrypts the message, the private key can decrypt the message, and the same applies if the private key encrypts the message, the public key decrypts the message.   The asymmetric key cryptosystem provides support to the digital signature technology.  The advantages of the asymmetric key algorithm include the generation of only one public-private key for new users, and the removal of the users easily.  Moreover, the key generation is required only when the private key of the user is compromised. The asymmetric key algorithm provides integrity, authentication, and non-repudiation.  The key distribution is a simple process in the asymmetric key algorithm.  The asymmetric key algorithm does not require a pre-existing relationship to provide a secure mechanism for data exchange (Abernathy & McMillan, 2016; Connolly & Begg, 2015; Maiwald, 2001; Stewart et al., 2015).

The limitation of the asymmetric key cryptosystem is the slow speed of operation.  Thus, many applications which require the secure transmission of the large volume of data employs the public key cryptographic system to establish a connection and then exchange a symmetric secret key.  The remainder of the session then utilizes the symmetric cryptographic approach. Figure 2 illustrates a comparison of symmetric and asymmetric cryptographic systems (Abernathy & McMillan, 2016; Connolly & Begg, 2015; Stewart et al., 2015).

Figure 2.  Comparison of Symmetric and Asymmetric Cryptographic Systems. Adapted from (Abernathy & McMillan, 2016; Stewart et al., 2015).

The Hashing Algorithm

The hashing algorithm produces message digests which are summaries of the content of the message.  It is challenging to derive a message from an ideal hash function, and two messages will unlikely produce the same hash value.  There are some of the more common hashing algorithm in use today including the Message Digest 2 (MD2), Message Digest 5 (MD5), Secure Hash Algorithm (SHA-0, SHA-1, and SHA-2), and Hashed Message Authentication Code (HMAC).  Unlike symmetric and asymmetric algorithms, the hashing algorithm is publicly known.  The hash functions are performed in one direction and using in reverse is not required.  The hashing algorithm ensures the integrity of the data as it creates a number which is sent along with the data.  When the data gets to the destination, this number can be used to determine whether even a single bit has changed in the data by calculating the hash value from the data which was received. The hashing algorithm also helps in protecting against undetected corruption (Abernathy & McMillan, 2016; Connolly & Begg, 2015; Stewart et al., 2015).

Attacks Against Encryption

The encryption systems can be attacked in three ways, through weaknesses in the algorithm, through brute-force against the key, or through a weakness in the surrounding system. When the algorithm is attacked through the weakness in the way that the algorithm changes plaintext into ciphertext so that the plaintext may be recovered without knowing the key.  The algorithm that has weaknesses of this type are rarely considered reliable enough for use.  The brute-force attacks are attempts to use every possible key on the ciphertext to find the plaintext.  On the average, 50% of the keys must be tried before finding the correct key.  The strength of the algorithm is then only defined by the number of keys that must be attempted.  Thus, the longer the key, the more significant the total number of keys and the larger the number of keys which must be tried until the correct key is found. The brute-force attacks will always succeed eventually if enough time and resources are used.  Thus, the algorithms should be measured by the length of time the information is expected to be protected even in the fact of a brute-force attack.  The algorithm is considered computationally secure if the cost of acquiring the key through brute-force is more than the value of the information being protected. The last encryption attack through weaknesses in the surrounding system can involve keeping the key in a file that has a password, but the password is weak and can be guessed easily (Maiwald, 2001).

References

Abernathy, R., & McMillan, T. (2016). CISSP Cert Guide: Pearson IT Certification.

Connolly, T., & Begg, C. (2015). Database Systems: A Practical Approach to Design, Implementation, and Management (6th Edition ed.): Pearson.

Maiwald, E. (2001). Network security: a beginner’s guide: McGraw-Hill Professional.

PCAST. (May 2014). Big Data and Privacy: A Technological Perspective.

Stewart, J., Chapple, M., & Gibson, D. (2015). ISC Official Study Guide.  CISSP Security Professional Official Study Guide (7th ed.): Wiley.

Woo, T. Y., & Lam, S. S. (1992). Authentication for distributed systems. Computer, 25(1), 39-52.